Being able to use a command-line build option like
debug=1 is handy,
but it can be a chore to write specific Python code
to recognize each such option
and apply the values to a construction variable.
To help with this,
SCons supports a class to
define such build options easily
and to read build option values from a file.
This allows you to control how the build options affect
construction environments.
The way you do this is by specifying
a file name when you call Options,
like custom.py in the following example: